Electrical stimulation lead with stiffeners having varying stiffness zones

ABSTRACT

In one embodiment, a neurostimulation lead comprises an elongated body of insulative material, comprising a first end portion and a second end portion; a plurality of terminals longitudinally positioned along the first end portion; a plurality of electrodes longitudinally positioned along the second end portion; a plurality of conductors electrically coupling the plurality of electrodes to the plurality of terminals; a flexible metal longitudinal stiffener positioned within the elongated body wherein the stiffener has a plurality of longitudinal zones and each zone has a different column strength, the column strength of one or more zones of the plurality of longitudinal zones being defined by cuts or gaps in the stiffener, the stiffener causing the neurostimulation lead to exhibit a greatest amount of column strength adjacent to one end portion of the elongated body and to transition to a lower column strength toward a medial portion of the elongated body.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.12/416,813, filed Apr. 1, 2009, now U.S. Pat. No. 8,244,372, whichclaims the benefit of U.S. Provisional Application No. 61/041,386 filedApr. 1, 2008, the disclosures of which are fully incorporated herein byreference.

TECHNICAL FIELD

The application is generally related to electrical stimulation leads forstimulation tissue of a patient and methods of their manufacture.

BACKGROUND

Neurostimulation systems are devices that generate electrical pulses anddeliver the pulses to nerve tissue to treat a variety of disorders.Spinal cord stimulation (SCS) is an example of neurostimulation in whichelectrical pulses are delivered to nerve tissue in the spine typicallyfor the purpose of chronic pain control. Other examples include deepbrain stimulation, cortical stimulation, cochlear nerve stimulation,peripheral nerve stimulation, vagal nerve stimulation, sacral nervestimulation, etc. While a precise understanding of the interactionbetween the applied electrical energy and the nervous tissue is notfully appreciated, it is known that application of an electrical fieldto spinal nervous tissue can effectively mask certain types of paintransmitted from regions of the body associated with the stimulatednerve tissue. Specifically, applying electrical energy to the spinalcord associated with regions of the body afflicted with chronic pain caninduce “paresthesia” (a subjective sensation of numbness or tingling) inthe afflicted bodily regions. Thereby, paresthesia can effectively maskthe transmission of non-acute pain sensations to the brain.

Neurostimulation systems generally include a pulse generator and one ormore leads. The pulse generator is typically implemented using ametallic housing that encloses circuitry for generating the electricalpulses, control circuitry, communication circuitry, a rechargeablebattery, etc. The pulse generation circuitry is coupled to one or morestimulation leads through electrical connections provided in a “header”of the pulse generator. Specifically, feedthrough wires typically exitthe metallic housing and enter into a header structure of a moldablematerial. Within the header structure, the feedthrough wires areelectrically coupled to annular electrical connectors. The headerstructure holds the annular connectors in a fixed arrangement thatcorresponds to the arrangement of terminals on a stimulation lead.

The terminals of a stimulation lead are electrically coupled to theconnectors within the header by manually pushing the proximal end of thestimulation lead into the header of the pulse generator. If thestimulation lead is improperly inserted into the header, the terminalsof the stimulation lead will not be properly aligned with the connectorsof the header and electrical pulses will not be properly conductedthrough the lead to electrodes for stimulation of tissue of the patient.

SUMMARY

In one embodiment, a neurostimulation lead comprises an elongated bodyof insulative material, comprising a first end portion and a second endportion; a plurality of terminals longitudinally positioned along thefirst end portion; a plurality of electrodes longitudinally positionedalong the second end portion; a plurality of conductors electricallycoupling the plurality of electrodes to the plurality of terminals; aflexible metal longitudinal stiffener positioned within the elongatedbody wherein the stiffener has a plurality of longitudinal zones andeach zone has a different column strength, the column strength of one ormore zones of the plurality of longitudinal zones being defined by cutsor gaps in the stiffener, the stiffener causing the neurostimulationlead to exhibit a greatest amount of column strength adjacent to one endportion of the elongated body and to transition to a lower columnstrength toward a medial portion of the elongated body.

The foregoing has outlined rather broadly certain features and/ortechnical advantages in order that the detailed description that followsmay be better understood. Additional features and/or advantages will bedescribed hereinafter which form the subject of the claims. It should beappreciated by those skilled in the art that the conception and specificembodiment disclosed may be readily utilized as a basis for modifying ordesigning other structures for carrying out the same purposes. It shouldalso be realized by those skilled in the art that such equivalentconstructions do not depart from the spirit and scope of the appendedclaims. The novel features, both as to organization and method ofoperation, together with further objects and advantages will be betterunderstood from the following description when considered in connectionwith the accompanying figures. It is to be expressly understood,however, that each of the figures is provided for the purpose ofillustration and description only and is not intended as a definition ofthe limits of the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of a lead according to a representativeembodiment.

FIG. 2 is a side view illustrating the lead of FIG. 1 coupled to a pulsegenerator.

FIG. 3 a is a detailed isometric view of an exemplary proximal stiffenerincorporating certain disclosed embodiments.

FIG. 3 b is a detailed isometric view of an exemplary distal stiffenerincorporating certain disclosed embodiments.

FIG. 4 a is a side view of an exemplary stiffener incorporating certaindisclosed embodiments.

FIG. 4 b is an isometric view of the exemplary stiffener of FIG. 4 a.

FIG. 5 a is a side view of an exemplary stiffener incorporating certaindisclosed embodiments.

FIG. 5 b is an isometric view of the exemplary stiffener of FIG. 5 a.

FIG. 6 a is a side view of an exemplary stiffener incorporating certaindisclosed embodiments.

FIG. 6 b is an isometric view of the exemplary stiffener of FIG. 6 a.

FIG. 7 is a flow chart illustrating a process of making certaindisclosed embodiments.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of thepresent application, reference will now be made to the embodiments, orexamples, illustrated in the drawings and specific language will be usedto describe the same. It will nevertheless be understood that nolimitation of the scope of the claims is thereby intended. Anyalterations and further modifications in the described embodiments, andany further applications of the principles of the embodiments asdescribed herein are contemplated as would normally occur to one skilledin the art to which the application relates.

Turning now to FIG. 1, there is presented one representative embodimentof a lead 100. As will be explained below, the lead 100 is generallyconfigured to transmit one or more electrical pulses from a pulsegenerator to a spinal nerve, a peripheral nerve, or other tissue. Thelead 100 comprises a proximal end 102 and a distal end 104. The lead 100further comprises a flexible lead body 106 that extends from proximalend 102 to the distal end 104. As will be explained in detail later, incertain embodiments, the lead body 106 may be formed of relatively softand compliant insulating materials such as silicone, polyurethane,polyethylene, polyamide, polyvinylchloride, PTFE, EFTE, or othersuitable materials known to those skilled in the art. In certainembodiments, one or more lumens (not shown) may extend through the leadbody 106 and, as will be explained later, may be used for housing one ormore stiffeners or stiffening stylettes. In the illustrative embodiment,there is a proximal end stiffener 108 and a distal end stiffener 110positioned within lumen(s) (not shown) of the lead body 106.

Adjacent to distal end 104 of lead 100 is a stimulation electrode region112 comprising, in this embodiment, eight stimulation electrodes 114.Adjacent to proximal end 102 of lead 100 is a connector region 116 that,in this embodiment, comprises eight terminals 118. For purposes ofillustration only, the lead 100 of FIG. 1 is shown with eightstimulation and eight terminals. As will be appreciated by those skilledin the art, any number of conductors, terminals, and electrodes may beutilized as desired to form lead 100. Generally, some embodiments havethe same number of stimulation electrodes as terminals. In thisillustrative embodiment, the stimulation electrodes and terminals areshown as metallic bands or rings.

One or more conductors (not shown) extending along a substantial portionof the lead body 106 electrically connect the terminals 118 to thestimulation electrodes 114. Although lead 100 is described as beingadapted for neurostimulation according to some embodiments, lead 100 canbe utilized for any suitable type of stimulation therapy, sensingapplication, or other medical application, such as functional electricalstimulation, cardiac stimulation, tissue ablation, gastric pacing, etc.

FIG. 2 illustrates the lead 100 connected to implantable pulse generator(IPG) 120 via a receptacle 122. As is well known in the art, animplantable pulse generator (IPG) is intended to be implanted within thebody of a patient to provide electrical stimulation to treat chronicpain or another condition of the patient. An exemplary implantable pulsegenerator is the EON® pulse generator available from AdvancedNeuromodulation Systems, Inc.

In this illustrative example, the lead 100 is connected to theimplantable pulse generator 120 via the receptacle 122. The lead 100 maybe detached from the pulse generator 120 as desired by applying adetaching force and removing proximal end 102 of the lead 100 from thereceptacle 122. Similarly, the lead 100 may be connected to the pulsegenerator 120 by pushing the proximal end 102 into the receptacle 122.

As illustrated, the terminals 118 are in electrical contact withelectrical connectors (not shown) within a header 123 of the pulsegenerator 120. A plurality of feedthrough wires (not shown) connect theelectrical connectors to pulse generating circuitry (not shown) withinthe pulse generator 120. The pulse generator 120 sends electrical pulsesto the electrical connectors, which are in electrical contact with theterminals 118. As previously discussed, the terminals 118 are themselvesin electrical contact with the stimulation electrodes 114 at distal endof lead 100 because conductors (not shown) electrically connect theterminals 118 with the stimulation electrodes 114.

Thus, the pulse generator 120 may generate and send electrical pulsesvia the lead 100 to the stimulation electrodes 114. In use, thestimulation electrodes 114 are placed at a stimulation site (not shown)adjacent to tissue of the patient suitable for electrical stimulation.The stimulation site may be located within the epidural space as oneexample. The pulse generator 120 generates and delivers the electricalpulses to one or more selected electrodes according to variousstimulation parameters (e.g., pulse amplitude, pulse width, pulsefrequency, electrode polarity, etc.). In certain embodiments, the pulsegenerator 120 receives the stimulation parameters and other controlsignals via wireless communication with an external programming device(not shown).

Turning now to FIG. 3 a, there is illustrated an isometric view of theproximal end 102 of the lead 100 with the lead body 106 and conductorsremoved for clarity. In this view, the stiffener 108 is shown as a tube124 having a proximal end portion 126 and a distal end portion 128. Thetube 124 could be made of Nitinol, stainless steel or otherbio-compatible materials. Tube 124 preferably possesses a substantiallyconstant diameter along its length. Although the tube 124 is used inthis description, in other embodiments, the stiffener could be formedfrom a rod, wire or other longitudinal member having a variety ofdifferent cross sectional shapes.

At the distal end portion 128, there is a spiral cut 130 through thewalls of the tube 124. As will be discussed later, the pitch of thespiral cut 130 varies as the spiral cut progresses from a distal end 132of the spiral cut towards the proximal end 134 of the spiral cut. Inthis illustrative example, the pitch of the spiral cut 130 is greatertowards the distal end 132 and decreases as the spiral cut progresstowards its proximal end 134. This varying pitch, in turn, affects andvaries the overall column strength of the tube 124 in the region of thespiral cut 130. As the pitch increases, the corresponding resistance tolateral and/or axial buckling for that portion of the tube 124decreases. For purposes of this application, resistance to lateraland/or axial buckling within a given longitudinal length will be definedto be “column strength.” For tubular structures having spiral cuts, thecolumn strength is a function of the remaining cross section area of thetube, the diameter of the tube, and the pitch of the spiral cut.

From an end user's perspective, a higher column strength increases the“pushability” of the stiffener 108 and decreases the “flexibility” ofthe stiffener. The flexibility of the tube portion is inverselyproportional to the column strength. In this example, therefore, theflexibility of the tube 124 increases towards the distal end 132 anddecreases towards the proximal end 134 of the spiral cut 130.

In the illustrative example, the portion of the tube 124 that runs fromits distal end 132 to the proximal end 134 of the spiral cut 130 is freeof any cuts in its sidewalls, and thus, has a maximum cross sectionalarea. The tube 124, therefore, has its greatest column strength in this“solid” region, which also includes the connector region 116 of the lead100 (See FIG. 1). So, in this example, the stiffener 108 may be thoughtof having at least two longitudinal zones. The first zone having aconstant column strength (from the proximal end 126 of the tube 124 tothe proximal end 134 of the spiral cut 130). The second zone is alongitudinal region having a reduced column strength. In theillustrative example, there are additional longitudinal zones ofdifferent column strengths which correspond to the varying change inpitch of the spiral cut 130.

This relatively large column strength of the first zone is advantageousbecause it allows a user to easily insert the proximal end 102 of thelead 100 into the receptacle 122 (FIG. 2) without excessive buckling.Without a stiffener, and especially for a stimulation lead having ahighly compliant lead body (see U.S. Publication No. 2007/0282411), thelead 100 would tend to buckle more easily and insertion into thereceptacle would be more difficult. Also, a relatively small implantablepulse generator adapted to accept a small diameter lead presents furtherdifficulty for the proper insertion of the lead into the header of thegenerator. Such difficulties may potentially cause terminals of lead 100to improperly couple or not couple at all to the electrical connectorswithin the header of pulse generator 120. Also, if a stiffener had aconstant column strength throughout its length, the stiffener wouldcreate a stress point at its distal end of the stiffener within therelatively soft and compliant material of the lead body 106 (FIG. 1). Astress point is created in the lead 100 when there is an abrupt changein stiffness in a portion of the lead 100 where the relatively greaterstiffness of a solid tube or wire meet a portion of the lead body 106made from compliant material. The stress point could lead to materialfailure of the lead body 106 and/or patient discomfort.

A stiffener having at least two zones of stiffness or column strengthcould provide the required column strength to help insert the proximalend 102 of the lead 100 into the receptacle 122 and may have theflexibility to reduce any stress points which typically occurs withinthe lead body 106 if a constant column strength tube were used. Astiffener with only two zones of stiffness would provide two stresspoints (around the point where change in stiffness occurs and at thedistal end). The magnitude of material stress within these two stresspoints would be significantly reduced when compared to the configurationhaving a single stress point. Similarly, a stiffener with multiple orvarying zones of stiffness allows a gradual transition—which effectivelyeliminates and/or greatly reduces the magnitude of material stresswithin any stress points.

In sum, the proximal lead stiffener 108 provides a maximum columnstrength in one zone from the proximal end 126 of the tube 124 to theproximal end 134 of the spiral cut 130, which allows for easy insertioninto a receptacle. In the second region from the proximal end 134 to thedistal end 132, there are additional zones where the column strength isgradually reduced to eliminate or greatly reduce any stress pointswithin the lead body 106.

FIG. 3 b is a detailed isometric view of the distal end portion 140 ofthe lead 100 with the lead body 106 and conductors removed for clarity.In this view, the distal end stiffener 110 is shown as a tube 136 havinga proximal end portion 138 and a distal end portion 140. The tube 136could be made of Nitinol, stainless steel or other bio-compatiblematerials. In this illustrative embodiment, there is a spiral cut 142through the walls of the tube 136. The pitch of the spiral cut 142 mayvary along the longitudinal length of the spiral cut 142. In thisillustrative example, the pitch of the spiral cut 142 may be greatertowards the proximal end portion 138 and decreases as the spiral cutprogress towards the distal end portion 140.

As explained above, this varying pitch affects and varies the overallcolumn strength of the tube 136 in the region of the spiral cut 142. Asthe pitch increases, the corresponding column strength for that portionof the tube 136 decreases. Similarly, the flexibility of the tubeportion increases because the flexibility is inversely proportional tothe column strength. Thus, by varying the pitch of the spiral cut 142,the tube 136 may have different longitudinal portions or zones in whicheach zone has a unique column strength. Furthermore, the zones couldvary from stiff to flexible to stiff, etc. depending on the application.For instance, in the region of the proximal end 138, there may be one ormore zones having a relatively reduced column strength to reduce stresspoints in the lead body 106 (FIG. 1) as described above. In other zoneswithin the stimulation electrode region 112, the column strength couldincrease or vary to make implantation easier for the surgeon or tocorrespond with anatomical features of the application and/or patient.For example, the distal end stiffener 110 may be five longitudinalzones, where each zone has a different column strength corresponding tosurgical implantation techniques and patient anatomy.

Turning now to FIG. 4 a, there is a side view of an example embodimentof a stiffener 144. FIG. 4 b is an isometric view of the exampleembodiment 144. As illustrated, the stiffener 144 has six longitudinalzones 146 to 152 of varying column strength created a spiral cut 154 (orlack thereof). In this example, the pitch of the spiral cut is maximumin the zone 151 (for example 0.02) and is minimum in the zone 147 (forexample 0.04). There is no cut in zone 146 and the tip portion 152.Thus, the column strength of the stiffener is maximum in zone 146,relatively stiff in zone 147 and is minimum in zone 151. Such aconfiguration could be used for a proximal end stiffener of a lead asdiscussed previously.

Although a spiral having varying pitch cut in a tube is but one exampleof a stiffener having a variable column strength, other implementationsare possible to provide variable column strength. For example,stiffeners having varying stiffness zones could also be created by usingdifferent patterns of cuts or slots formed in the longitudinal member.The stiffener shown in FIGS. 5 a and 5 b is one such example.

FIG. 5 a is a side view of another embodiment of a stiffener 156. FIG. 5b is an isometric view of the stiffener 156. In this example embodiment,the column strength varies due a series of alternating lateral cuts orslots made within the walls of a tube 158. In this example embodiment,the stiffener 156 has five longitudinal zones 160 to 164 of varyingcolumn strength created by a change in spacing of the lateral cuts. Asillustrated in FIG. 5 b, there may be a first series of lateral slots orcuts 166 and a second series of opposing cuts 168 positioned across fromthe lateral cuts 166 (forming a first plurality of pairs of opposinglater cuts). Longitudinally spaced within the series of lateral cuts 166and 168, there may be another series of interspersed cuts 170 and acorresponding series of opposing lateral cuts 172 forming a secondplurality of pairs of opposing lateral cuts. In certain embodiments, thelateral cuts 170 and 172 may be orientated substantially perpendicularto the lateral cuts 166 and 168. In other embodiments, the lateral cutscould be orientated at other angles or angles which vary along thelength of the stiffener 156.

In this example, the spacing of the lateral cuts is maximum in the zone163 (for example 0.02 inch) and is minimum in the zone 161 (for example0.03 inch). In this embodiment, zone 162 is a transition zone.Furthermore, there are no cuts in zone 160 and the tip portion 164.Thus, the column strength of the stiffener 156 is maximum in zone 160,relatively stiff in zone 161 and is minimum in zone 163. Such aconfiguration could also be used for a proximal end stiffener of a leadas discussed previously.

Turning now to FIG. 6 a, there is a side view of an example embodimentof a stiffener 180 which may be used at a distal end of a lead. FIG. 6 bis an isometric view of the example embodiment 180. As illustrated, thestiffener 180 has five longitudinal zones 182 to 186 of varying columnstrength created a spiral cut 188 (or lack thereof). In this example,however, the pitch of the spiral cut 188 varies within certainlongitudinal zones.

In certain embodiments, there is no cut in the end portions (zone 182and the tip portion 186). In zone 183, the pitch of the spiral cut 188varies from a lesser value at a proximal end 190 of the zone to agreater value at a distal end 192 of the zone. In zone 184, the pitchmay remain constant. In zone 185, the pitch of the spiral cut 188 mayvary from a greater value at the proximal end 194 to a lesser value atthe distal end 196 of the zone. Consequently, the column strength of thestiffener 188 is maximum in zones 182 and 186. In zone 183, the columnstrength varies from a relatively low value at the proximal end 190 ofthe zone to a relatively high value at the distal end 192. The columnstrength remains constant in zone 184. In zone 185, the column strengthvaries from a relatively higher value at the proximal end 194 of zone185 to a lower value at the distal end 196.

Such a configuration for a distal end stimulation stiffener may keep thelead from buckling when implanted in the dorsal column due to gravity orpatient movements. In some embodiments, the stimulation end stiffenermay also reduce the likelihood of lead buckling off the needle duringimplant and pushing. In certain embodiments, the stimulation endstiffener may make it easier to steer the lead. In certain regions, thecolumn strength of the end of the lead may be weaker so that itcompliments and complies with the bend of the stylet.

The stiffener 180 may be dimensioned to conform to the anatomy of apatient. By way of an illustrating example, in a certain embodiment of atubular stiffener made from a superelastic Nitinol alloy having asimilar configuration to that illustrated in FIGS. 6 a and 6 b, theoverall length of the stiffener could be approximately 7.8 inches. Theexterior diameter of the stiffener may be 0.021″ and an interiordiameter of 0.017.″ In such an example, the spiral cut 188 may have awidth of 0.003″. The zone 183 may have a length of approximately 1.96inches. The pitch of the spiral cut 188 may vary from 0.02″ inches atthe proximal end 190 of the zone 183 to 0.08″ at the distal end 192 ofthe zone. The pitch of the spiral cut 188 in zone 184 may be 0.1″. Inzone 185, the pitch of the spiral cut 188 may vary from 0.08″ at theproximal end 194 of the zone to 0.02″ at the distal end 196 of the zone.The foregoing dimensions are provided by way of example only, and arenot meant to limit the scope of the present invention in any manner.

Various methods of making lead bodies with conductors are known in theart. Certain methods of making a lead body with conductors are disclosedin U.S. Publication No. 2005/00027340, entitled “System and Method forProviding a Medical Lead Body having Dual Conductor Layers, ” filed onJul. 29, 2003 and in U.S. Pat. No. 6,216,045, entitled “Implantable Leadand Method of Manufacture, ” filed on Apr. 26, 1999, the disclosures ofwhich are hereby incorporated by reference for all purposes. In oneembodiment, the stimulation lead is adapted to exhibit appreciableelongation under relatively low stretching forces. For example, thestimulation lead may be adapted to elongate at least 15%, 25%, or morewhen a relatively low stretching force (e.g., 1 or 2 pounds or less) isapplied to the lead. Fabrication of stimulation leads adapted in thismanner is described in U.S. Publication No. 2007/0282411 entitled“Compliant Electrical Stimulation Leads and Methods of Fabrication,”filed on Mar. 30, 2007, the disclosure of which is incorporated hereinby reference for all purposes.

FIG. 7 is a process flow chart illustrating one embodiment of a method700 for making a lead incorporating various features discussed above.The process begins at step 701. In step 702, an inner layer of extrusionmaterial may be placed on a mandrel to begin forming the lead body. Aplurality of conductors may be provided where each conductor is coatedwith extrusion material. Each coated conductor may be wrapped around theinner layer of the extrusion material on the mandrel (step 704). Anouter layer of extrusion material may then be placed over the pluralityof conductors (step 706). Heat shrink tubing is then placed over theouter layer and the lead body assembly may be heated to melt theextrusion material. The melted extrusion material is compressed aroundthe plurality of conductors as the heat shrink tubing shrinks. The leadbody may then be cooled and the heat shrink tubing may be removed. Thesolidified extrusion material forms the lead body. The lead body maythen be removed from the mandrel which leaves a longitudinal lumen inthe lead body (step 708).

In step 710, stiffeners incorporating various aspects disclosed abovemay now be inserted into the longitudinal lumen. In certain embodiments,the stiffeners may be inserted into both the proximal ends and thedistal ends. In other embodiments, a stiffener may only be inserted intoeither the proximal or distal end depending on the application for thelead.

In step 712, the conductors may be prepared to electrically connect withelectrodes. Such preparation may include laser ablating the electrodesites on the proximal and distal ends of the lead body. Once the sitesare ablated, the conductors may be pulled to the surface.

In some embodiments, distal ends of a plurality of ribbons correspondingto the number of electrodes may be laser welded to conductors at theelectrode sites. (step 714). In certain embodiments, the electrodes maynow be slid over the ribbons. In step 716, the stiffener depth may nowbe adjusted. The electrodes may then be longitudinally positioned alongthe lead body (step 718). In certain embodiments, a fixture indicatingthe proper spacing may be used. Once in place, the electrodes may bepre-crimped.

The electrodes may then be swaged onto the lead (step 720). Thestiffener provides a solid center which provides the necessarycompression needed to swage the respective electrode over the lead body.After the electrodes are compressed by the swaging, the proximal ends ofeach ribbon may be welded to an edge of a corresponding electrode (step722). In step 724, additional extrusion material may then be placed overthe proximal and distal ends of the lead. The leads may then be annealed(step 726). In step 728, final preparation of the leads, includingvarious testing, may then be accomplished using methods known to thoseskilled in the art. In certain embodiments, the process ends at step730.

In some embodiments, therefore, leads may be manufactured integral withstiffeners having varying zones of stiffness. When used as described inthe above manufacturing process, such stiffeners provide the necessarycompression force to allow swaging of the electrodes to the leads whilereducing the likelihood of undesirable stress points developing withinthe lead at a later point in time.

In other embodiments, electrodes may be coupled to the leads using othermethods known to those skilled in the art. In such embodiments,stiffeners having varying zones of stiffness may be used to enhance thesteerability of the lead during implantation or during coupling of thelead to the pulse generator. In such embodiments, the leads do not haveto be formed integral with the stiffeners. The stiffeners may beinserted into the central lumen of the lead at a later time.

In certain embodiments, the leads and stiffeners could be provided aspart of a kit. In such embodiments, the leads may have a proximalstiffener to aid in the coupling of the lead to a pulse generator. Theleads may also be supplied with a plurality of stiffeners, where eachstiffener has different length longitudinal zones of stiffnesscorresponding to the likely sizes and shapes of patient anatomy. Incertain embodiments, a plurality of stylets may also be used with asingle stiffener. For instance, the stylets may be used in conjunctionwith a distal end stiffener and may have complimentary structuralproperties. The stylets may have longitudinal stiffness zones which aredesigned to compliment the longitudinal stiffness zones of thecorresponding stiffeners to increase steerability during implantation.Upon removal of the stylet, the end stiffener may then have longitudinalstiffness zones which closely correspond with a patient's anatomy toreduce buckling during use. Such a kit would allow a surgeon to havegreater flexibility in choosing the correct stiffener and stylet to usein an individual patient.

Once implanted, various disclosed embodiments of the distal endstimulation stiffener may keep the lead from buckling when implanted inthe dorsal column due to gravity or patient movements. Specifically, inthe space between the distal stimulation end and an anchor. Buckling inthis area is undesirable because if the lead buckles, the stimulationend will lose its position and the effectiveness of stimulation may bediminished. In some embodiments, the stimulation end stiffener may alsoreduce the likelihood of lead buckling off the needle during implant andpushing. In certain embodiments, the stimulation end stiffener may makeit easier to steer the lead. In certain regions, the column strength ofthe end of the lead may be weaker so that it compliments and complieswith the bent of the stylet. Additionally, various embodiments of thestimulation end stiffener may assist the physician to steer throughimpediments or obstructions during the implantation procedure.

Any advantages and benefits described above may not apply to allembodiments of the invention and may not apply to all of the claims. Theforegoing description of the embodiments of the invention has beenpresented for the purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed. Many combinations, modifications and variations are possiblein light of the above teaching. Undescribed embodiments which haveinterchanged components are still within the scope of the presentinvention. It is intended that the scope of the invention be limited notby this detailed description, but rather by the claims appended hereto.

The abstract of the disclosure is provided for the sole reason ofcomplying with the rules requiring an abstract, which will allow asearcher to quickly ascertain the subject matter of the technicaldisclosure of any patent issued from this disclosure. It is submittedwith the understanding that it will not be used to interpret or limitthe scope or meaning of the claims.

What is claimed:
 1. A method of fabricating a neurostimulation lead,comprising: forming a lead body of insulative material, the insulativematerial enclosing a plurality of conductors extending along asubstantial portion of a length of the lead body; providing a pluralityof electrodes on a distal end of the lead body; providing a plurality ofterminals on a proximal end of the lead body, the plurality of terminalsbeing electrically connected to the plurality of electrodes through theplurality of conductors; and adapting the proximal end of the lead bodyto possess a modified amount of column strength by providing a flexiblemetal longitudinal stiffener within the lead body with the stiffenerhaving at least a first and second region with the first region beingsolid walled and the second region having at least one spiral cut, thestiffener causing the neurostimulation lead to exhibit a greatest amountof column strength adjacent to the proximal end of the lead body and totransition to a lower column strength toward a medial portion of thelead body.
 2. The method of claim 1 wherein the column strength of thelongitudinal stiffener is varied continuously along the spiral cut. 3.The method of claim 1 wherein a pitch of the spiral cut is varied alonga substantial length of the second region of the longitudinal stiffener.4. The method of claim 1 wherein the longitudinal stiffener comprises: afirst plurality of pairs of opposing lateral slots longitudinally spacedat a first distance along a first stiffness zone; a second plurality ofpairs of opposing lateral slots longitudinally spaced at the firstdistance along the first stiffness zone, wherein the second plurality ofpairs of opposing lateral slots are longitudinally interdispersed amongthe first plurality of pairs of opposing lateral slots and are angularlyoffset about the longitudinal axis from the first plurality of pairs ofopposing lateral slots, a third plurality of pairs of opposing lateralslots longitudinally spaced at a second distance along a secondstiffness zone, and a fourth plurality of pairs of opposing lateralslots longitudinally spaced at the second distance along the secondstiffness zone, wherein the fourth plurality of pairs of opposinglateral slots are longitudinally interdispersed among the thirdplurality of pairs of opposing lateral slots and are angularly offsetabout the longitudinal axis from the third plurality of pairs ofopposing lateral slots.
 5. The method of claim 1 wherein the lead bodyappreciably elongates in response to stretching forces.
 6. The method ofclaim 5 wherein the lead body elongates more than 15% in response to astretching force of two pounds or less.